The permanent alteration of the hair colour by the application of hair dyes is well known. In order to provide the consumer with the shade and the intensity of colour desired, a complex chemical process is utilized. Permanent hair dyeing formulations typically comprise oxidative hair dye precursors, which can diffuse into the hair through the cuticle and into the cortex where they then react with each other and a suitable oxidizing agent to form the end dye molecules. Due to their larger size, the resultant molecules are unable to readily diffuse out of the hair during subsequent washing with water and/or detergents; hence delivering a consumer-desired permanency of colour. This reaction typically takes place at approximately pH 10 in the presence of an alkalizing agent and an oxidizing agent. Typically an oxidizing composition (also called developer and/or oxidizing component) comprising the oxidizing agent and a dye composition (also called tint or dye component) comprising the alkalizing agent and the precursors dye molecules are mixed shortly before use. The consumer repeats this process regularly in order to maintain the desired hair colour and shade and the intensity of colour and to ensure continual, even coverage of the hair including coverage of new hair growth.
Hair colouring formulations comprising one or more oxidative dye precursor(s) selected from the group consisting of 2-methoxymethyl-p-phenylenediamine, cosmetically acceptable salts thereof and mixtures thereof have been developed in the past. The inventors have noticed that when such hair colouring formulations are applied onto hair, they typically require a higher concentration of oxidative dye precursor(s) than formulations comprising other types of oxidative dye precursor(s) such as p-phenylene diamine or toluene-2,5-diamine to achieve a desired hair colour intensity. However, by increasing the concentration of oxidative dye precursor(s) comprised by these formulations, the end colour result along the entire length of hair (from roots to tips) coloured with such formulations may not always be homogeneous.
Therefore, there still exists a need for achieving a desired colour intensity of hair colored with these formulations without compromising the evenness of the overall end colour result.
The inventors have surprisingly found that by adding oil to a formulation comprising one or more oxidative dye precursor(s) selected from the group consisting of 2-methoxymethyl-p-phenylenediamine, cosmetically acceptable salts thereof and mixtures thereof, it is possible to reduce the concentration of oxidative dye precursor(s) comprised by these formulations in order to achieve a desired hair colour intensity. Consequently, a more even overall end colour result may be obtained.